The invention relates to broadband antennas, and especially to a compact, multiply-polarized log-periodic antenna.
Log-periodic broadband antennas are known that consist of four radial antenna arms, 90xc2x0 apart around a common center, from which antenna elements branch off alternately to left and right of each arm. The lengths of the elements, and the spacings between them, increase logarithmically away from the center. The signal feed is usually at the center, with two opposite arms being combined to provide a linearly polarized antenna, or all four to provide a circularly polarized antenna. In order to handle lower frequencies with a physically small antenna, the antenna elements on adjacent arms are sometimes interleaved.
According to one aspect of the invention, there is provided an antenna comprising a dielectric sheet, and a pair of feed stems facing one another on opposite sides of the sheet. A plurality of antenna elements extend away from each feed stem, each antenna element forming a pair with an antenna element on the other feed stem.
According to another aspect of the invention, there is provided an antenna comprising a feed stem and a plurality of antenna elements extending laterally from the feed stem, wherein the antenna elements are of zig-zag form such that the electrical length of each element is greater than the distance between its ends.